Microsurgical procedures frequently require precision cutting and/or removing various body tissues. For example, certain ophthalmic surgical procedures require cutting and removing portions of the vitreous humor, a transparent jelly-like material that fills the posterior segment of the eye. The vitreous humor, or vitreous, is composed of numerous microscopic fibrils that are often attached to the retina. Therefore, cutting and removing the vitreous must be done with great care to avoid traction on the retina, the separation of the retina from the choroid, a retinal tear, or, in the worst case, cutting and removal of the retina itself. In particular, delicate operations such as mobile tissue management (e.g. cutting and removal of vitreous near a detached portion of the retina or a retinal tear), vitreous base dissection, and cutting and removal of membranes are particularly difficult.
The use of microsurgical cutting probes in posterior segment ophthalmic surgery is well known. These cutting probes typically include a hollow outer cutting member (the needle), a hollow inner cutting member (the cutter) arranged coaxially with and movably disposed within the hollow outer cutting member, and a port extending radially through the outer cutting member near the distal end thereof. Vitreous humor and/or membranes are aspirated into the open port, and the inner member is actuated, closing the port. Upon the closing of the port, cutting surfaces on both the inner and outer cutting members cooperate to cut the vitreous and/or membranes, and the cut tissue is then aspirated away through the inner cutting member.
The inner cutting member (or cutter) in conventional vitrectomy cutting probe systems typically connects with a larger tube within the probe via a coupling device. With each cutting cycle, the inner cutting member (or cutter), the coupling device, and the larger tube all axially displace by an amount equal to the cutting stroke length, thereby cutting the vitreous that entered the port. However, the cutting motion also results in a change of the internal fluid volume of the ophthalmic probe. This is due to the difference in internal cross-sectional area between the cutter and the larger tube in conjunction with the axial motion of this transition. The volume change may cause pressure pulses and fluid agitation which could result in fluid pumping, and due to the vacuum present, could drive some gas out of solution, thereby producing bubbles. Further, while most of the excess volume may propagate up the aspiration tube, some of the volume may manifest itself as pulses or even a reversal of flow during vitrectomy cutting. It may also create some agitation that results in gas coming out of solution.
The present disclosure is directed to addressing one or more of the deficiencies in the prior art.